Field of the Invention
The present invention concerns a process for the hydrothermal treatment of high molar mass biomaterials, which further have high carbon contents. In addition, the invention concerns the structural carbon products thus obtained, as well as the applications of these products.
Description of Related Art
Carbonization is the general term of the frequently used procedures for converting biomaterials into products of higher carbon content. These procedures can utilize heating, whereby it can be carried out as a type of pyrolysis. However, also water, and sometimes catalysts, can be applied.
Hydrothermal carbonization (HTC) is a technology involving the use of moderate heat and moderate pressure. The technology has been applied since the early 20th century. It is based on an exothermal reaction used to convert biomaterials into coal-containing products in the aqueous phase, utilizing moderately elevated temperatures and pressures, while producing minimal CO2 emissions. Hydrothermal liquefaction (HTL) is a similar conversion process, which utilizes process conditions (temperatures and pressures) that are slightly harsher than in the HTC process.
Procedures of these types have been described in various publications in the past. JP 2011178851 discloses a process for the hydrothermal treatment of lignin at 300° C. to produce carbonized lignin, which can be used for electrical wires or cable jacketing. DE 102009015257, in turn, discloses a process for the hydrothermal carbonization of biomaterials of plant and animal origin (including wood chips) at a pressure of at least 5 bars and a temperature of up to 100° C., wherein the process conditions have improved in terms of heat and water supply.
Frequently, catalysts are also used, particularly to speed up the conversion, or to reduce the required temperature or pressure. WO 2008095589 A1 concerns a process for the hydrothermal carbonization of biomass at elevated pressure and preferably at a temperature of 140-240° C. using a catalyst, wherein the process conditions have been improved in terms of the time needed for the conversion. WO 2009127727 A1, in turn, concerns a two-step process for the hydrothermal carbonization of biomass, including any plant and animal-derived material, to obtain a coal-like material, wherein the first step is carried out at using heating, preferably to a temperature of 210-250° C., and the second step is carried out using a catalyst (a polymerization initiator) whereby the temperature can be lowered. In the publication, the process is said to be improved, among others, in terms of the time needed for the conversion and in terms of quality control.
Many types of biomasses, also those including lignin, have been subjected to HTC in the past. In fact, unlike other common processes, such as combustion, HTC allows the use of biomass raw materials with relatively high water contents, such as wood materials, including paper or board pulp as well as various plant-based waste materials. An article by Zhang, J., et al. (Journal of Chemical Technology and Biotechnology (2011), 86(9), 1177-1183) describes a method for producing spherical lignin and spheroidal microporous or mesoporous activated carbon from pulping black liquor. Similarly, Kang et al. (2012) concerns a process for the hydrothermal carbonization at 220-285° C. of black liquor having a crude lignin content of 30 wt % using formaldehyde as a polymerization agent to produce hydrochar with an improved yield and carbon recovery efficiency.
Thus, many attempts to improve such hydrothermal processes have been made in the past. Partly due to the fact that these procedures can be applied on biomasses with high water-contents, no reason has been found for separating the biomass into fractions. In fact, it has been considered advantageous to utilize all the carbon-containing waste-components of these available biomasses in the process to reduce the amount of further waste.
However, the present inventors have found that an improved yield and an improved efficiency can be obtained by utilizing only the high molar mass fractions of biomasses as the starting materials of the hydrothermal treatment.
The new procedure of the present invention has also been surprisingly found to result in an improved morphological control and better defined physico-chemical properties of the products (e.g. in terms of surface area, carbon content, density, size and shape).